Free electron energy$|$ Problem

Imagine two free electrons that collide elastically in an acidic solution.$$ Before the collision, electron A was moving, but electron B was stationary.$$ After the collision, electron A has a speed of $400$ m$/$s$,$ and electron B has a speed of $200$ m$/$s$.$ What was the kinetic energy of electron A before the collision?$$

Group of answer choices

$447$ J

$100,000$ J

$9\mathrm{.}1$x$10-26$J

$4\mathrm{.}1$x$10-28$J